Proximity and sterics play a large role in polymerization and polymer chemistry. In the development and testing of bimetallic polymerization catalysts where the two metal centers are held on the same side of the molecule by a rigid ligand framework, the proximity of the second metal changes reactivity at the first. The resulting enhancements of polar group tolerance or isoselecitivity in olefin polymerization are not observed in related bimetallic systems with distal metal centers or in monometallic analogues. In cross metathesis between poly(cyclooctene) chains, high E-stereoregularity and head-to-tail regioregularity are achieved with Grubbs second or third generation catalysts when there is allylic substitution directing reactivity through steric effects. In multiblock polymers, the proximity of incompatible blocks due to a covalent connection engenders frustration in the system. This frustration can produce interesting and complicated morphologies in the bulk and in thin films where thermodynamic penalties are expected to minimize the intermaterial dividing surface. These projects demonstrate the power of proximity in directing reactivity, selectivity, and equilibria in polymer science.
Madalyn Radlauer, Theodor Agapie, and Marc Hillmyer. "Proximal effects in bimetallic catalysts for olefin polymerization, in cross metathesis of poly(3-R-cyclooctenes), and in multiblock polymers" American Chemical Society 252nd National Meeting (2016).